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dc.contributor.advisorHarriss, Wendy Michelleen
dc.contributor.advisorLawson, J.en
dc.contributor.advisorPollard, Judith Maryen
dc.contributor.authorRijken, James D.en
dc.description.abstractWhen heated, lithium fluoride (LiF) crystals that have been exposed to ionising radiation emit light proportional to their absorbed dose, in a phenomenon known as thermoluminescence. This phenomenon has applications in dose measurement for radiation research, clinical cancer treatment and personal safety dose monitoring. LiF thermoluminescent dosimeters (TLDs) have a response that is dependent on the energy spectrum of the incoming radiation. Therefore, TLDs need to be calibrated for each spectrum they are exposed to, in order to be used as accurate dosimeters. The TLD energy response was investigated specifically for a set of TLD700:LiF(Mg,Ti) chips for a range of clinical radiation beams used for Radiation Oncology treatments, including Linear Accelerator electron and x ray beams, superficial x rays and an 192Ir brachytherapy source. Once calibrated, the TLD chips were used to verify the accuracy of the high dose rate (HDR) brachytherapy treatment planning system, Oncentra Prostate. To carry out this investigation, the TLD700:LiF chips were exposed to known doses of radiation from nominal 6 MV and 18 MV photon beams as well as nominal 6 MeV, 9 MeV, 12 MeV, 16 MeV and 20 MeV electron beams from a Linear Accelerator. The TLDs were read and the response from each beam was normalised to that from the 6 MV beam. The TLDs were also exposed to a series of known doses from a superficial x ray machine with peak energies of 30 kVp, 40 kVp, 50 kVp, 80 kVp, 100 kVp, 120 kVp and 150 kVp. The response to these was similarly compared to the response from the 6 MV beam with equivalent dose. The TLDs were then calibrated for exposure to an iridium-192 source, used for HDR brachytherapy. The delivered dose was determined by Monte Carlo simulation of the experimental setup using the package GEANT4. The TLDs were exposed to the source in air and at varying depths in water. The response for each of these scenarios was compared to the response from the 6 MV beam. Finally, the calibrated TLDs were used to verify the Oncentra Prostate treatment planning system by exposing them within a water phantom. A realistic prostate treatment plan was created on a reconstructed ultrasound image data set of the phantom. The treatment plan was delivered to the phantom with the TLD chips at known locations. The dose to the TLDs was compared to the simulated doses at corresponding points in the phantom within Oncentra Prostate. Results show that, relative from the response to the 6 MV beam, TLDs under-respond by approximately 4% for electron beams and by approximately 3% for the 18 MV photon beam. An over-response of up to 54% was observed for SXR beams with peak energies between 40 and 150 kV. The TLD700 chips over-respond by approximately 11% when exposed to the gamma spectrum of ¹⁹²Ir in air and were shown to have a depth dependent response in water. The TLDs used to verify Oncentra Prostate produced a dose ratio of DTLD/DOCP that was not statistically different from the expected value of 1.0 at the 5% significance level. With confidence level 95%, the true value of DTLD/DOCP was shown to lie in the confidence interval 1.023±0.041. Therefore, Oncentra Prostate was considered verified for the full prostate treatment. When compared directly with Monte Carlo predictions, the dose ratio values of DMC/DOCP were also found not to be statistically different to 1.0 at the 5% significance level for a single dwell treatment plan. With confidence level 95%, the true value of DMC/DOCP was shown to lie in the confidence interval 1.029±0.064, so Oncentra Prostate was also considered verified for the single source dwell treatment plan.en
dc.subjectTLD; energy dependence; Ir192; high dose rate; brachytherapy; treatment planning system; Oncentra Prostateen
dc.titleCalibration of TLD700: LiF for clinical radiotherapy beam modalities and verification of a high dose rate brachytherapy treatment planning system.en
dc.contributor.schoolSchool of Chemistry and Physicsen
dc.provenanceThis electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the author of this thesis and do not wish it to be made publicly available, or you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
dc.description.dissertationThesis (M.Phil.) -- University of Adelaide, School of Chemistry and Physics, 2014en
Appears in Collections:Research Theses

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